1. Field of the Invention
The present invention relates generally to track following positioning systems, and more particularly to systems for demodulating servo signals within an amplitude modulation track following servo environment.
2. Description of the Prior Art
Digital data are conventionally stored on magnetic medium in the form of flux transitions on the surface of the medium. Data recovery consists of determining the presence, and relative timing, of such flux transitions. Optimal operation of a recording device therefore depends upon the proper orientation and position of the magnetic head. Otherwise, the use of an improperly oriented and positioned recording head may result in the information being recorded in a manner that cannot be accurately retrieved on playback. Similarly, an improperly oriented or positioned playback head may result in the inaccurate retrieval of information even if the information was properly recorded. In either case, the integrity of the information storage system may be compromised and information may be lost.
Furthermore, as the density of the storage of digital information on magnetic surfaces continues to increase, it has become more difficult to accurately and reliably determine the presence or absence of such flux transitions. Track density is typically increased through the use of narrower track widths, closer track spacing, or both. As a result, there is very little tolerance for error in the orientation and position of the magnetic head within the recorder.
Recently, positioning systems employing amplitude modulation (AM), such as the positioning system employed by 3M of Minneapolis, Minn. utilizing Magnus 10.3 tapes, have been used to maintain the position of a magnetic tape head in alignment with tracks of data stored in magnetic medium. The tape head is aligned on-track when it is positioned at a desired location on the tape.
Regardless of the method used for writing position sensitive information (servo information) on the tape, information can be corrupted, or even destroyed, by impulse noise, dropouts, or amplitude modulation noise. Impulse noise can be generated by fast transitions from logic elements and other fast switching circuits coupling into the read head for servo. Dropouts are due to manufacturing imperfections and wear to the tape. Amplitude modulation noise can come from variations in head to tape contact. A special case of this is magnetic-resistive (MR) thermal noise generated by sudden cooling of the MR element in the MR head as it comes into more intimate contact with the tape. MR thermal noise causes simultaneous impulse and amplitude modulation noise. MR thermal noise is likely to occur at higher frequencies than the tape wander that the track following positioning system tracks.
What is needed is a track following positioning system that generates reliable servo error signals for accurate head positioning and that is tolerant to impulse noise, dropouts, and amplitude modulation noise.